The answer to that question depends on what we as a society are willing to do to get fossil fuels. How much are we willing to damage the environment to extract and transport fossil fuels? How much are we willing to raise atmospheric greenhouse gas levels and further alter climate? The Keystone Pipeline would bring crude oil from tar sands to the U.S., but for the time being, that project is on hold.

Fossil Fuel Reserves

Fossil fuels provide about 85% of the world’s energy at this time. Worldwide fossil fuel usage has increased many times over in the past half century (coal – 2.6x, oil – 8x, natural gas – 14x) because of population increases, because of increases in the number of cars, televisions, and other fuel-consuming uses in the developed world, and because of lifestyle improvements in the developing world.

The amount of fossil fuels that remain untapped is unknown, but can likely be measured in decades for oil and natural gas and in a few centuries for coal (
Figure
above
).

Alternative Fossil Fuels

As the easy-to-reach fossil fuel sources are depleted, alternative sources of fossil fuels are increasingly being exploited (
Figure
below
). These include oil shale and tar sands.
Oil shale
is rock that contains dispersed oil that has not collected in reservoirs. To extract the oil from the shale requires enormous amounts of hot water.
Tar sands
are rocky materials mixed with very thick oil. The tar is too thick to pump and so tar sands are strip-mined. Hot water and caustic soda are used to separate the oil from the rock.

A satellite image of an oil-sands mine in Canada.

The environmental consequences of mining these fuels, and of fossil fuel use in general, along with the fact that these fuels do not have a limitless supply, are prompting the development of alternative energy sources in some regions.

Summary

Easy to get at fossil fuels are running out, but there are other sources that are harder to get at that are still available.

Oil shales and tar sands are two of the alternative sources of fossil fuels that are much in the news.

The need for fossil fuels continues to grow as people in the developed work use more and more people in the developing world want them.